vfs: give all vfs an options attribute by default Multiple code path assume vfs have an options attribute, including the vfs module itself. So for consistency we explicitly add one to all vfs. This will prevent various crash in the next changesets. Differential Revision: https://phab.mercurial-scm.org/D6935

revlog: explicitly set revlogv0 in vfs options Relying on having an attribute or not for something so fundamental seems too fragile to me. (And indeed I had issue with that later in this series). So we explicitly record the fact the repository use revlog-v0. Differential Revision: https://phab.mercurial-scm.org/D6934

context: clarify the various mode in the _copies property cache The previous code was compact but a bit dense. The new proposed code deal with each mode separately, there are some duplicated lines, but the meaning of each mode stand out. One of the benefit it to make it simpler to add further mode in the future. Differential Revision: https://phab.mercurial-scm.org/D6933

context: clarify the various mode in the filesremoved method The previous code was compact but a bit dense. The new proposed code deal with each mode separately, there are some duplicated lines, but the meaning of each mode stand out. One of the benefit it to make it simpler to add further mode in the future. Differential Revision: https://phab.mercurial-scm.org/D6932

context: clarify the various mode in the filesadded method The previous code was compact but a bit dense. The new proposed code deal with each mode separately, there are some duplicated lines, but the meaning of each mode stand out. One of the benefit it to make it simpler to add further mode in the future. Differential Revision: https://phab.mercurial-scm.org/D6931

copies: expand the logic of usechangesetcentricalgo Using intermediate variable is clearer and will make is simple to expand the logic. Differential Revision: https://phab.mercurial-scm.org/D6930